During Japan's annexation of Korea, "Hanseong" (漢城) was renamed to "Keijō" (京城) by the Imperial authorities to prevent confusion with the hanja '漢' (a transliteration of an ancient Korean word "Han" (한) meaning "China"), which refers to Han people or the Han dynasty and in Japanese is a term for "China".[27]

Its current name originated from the Korean word meaning "capital city", which is believed to have descended from an ancient word, Seorabeol (Hangul: 서라벌; Hanja: 徐羅伐), which originally referred to Gyeongju, the capital of Silla.[28] Ancient Gyeongju was also known in documents by the Chinese-style name Geumseong (金城, literally "Gold Castle/City" or "Metal Castle/City"), but it is unclear whether the native Korean-style name Seorabeol had the same meaning as Geumseong.

Settlement of the Han River area, where present-day Seoul is located, began around 4000 BCE.[32]

Seoul is first recorded as Wiryeseong, the capital of Baekje (founded in 18 BCE) in the northeastern Seoul area.[32] There are several city walls remaining in the area that date from this time. Pungnaptoseong, an earthen wall located southeast Seoul, is widely believed to have been at the main Wiryeseong site.[33] As the Three Kingdoms competed for this strategic region, control passed from Baekje to Goguryeo in the 5th century, and from Goguryeo to Silla in the 6th century.[34]

In the 11th century Goryeo, which succeeded Unified Silla, built a summer palace in Seoul, which was referred to as the "Southern Capital". It was only from this period that Seoul became a larger settlement.[32] When Joseon replaced Goryeo, the capital was moved to Seoul (also known as Hanyang or Hanseong), where it remained until the fall of the dynasty. The Gyeongbok Palace, built in the 14th century, served as the royal residence until 1592. The other large palace, Changdeokgung, constructed in 1405, served as the main royal palace from 1611 to 1872.[32] After Joseon changed her name to the Korean Empire in 1897, Hwangseong also designated Seoul.

Originally, the city was entirely surrounded by a massive circular stone wall to provide its citizens security from wild animals, thieves and attacks. The city has grown beyond those walls and although the wall no longer stands (except along Bugaksan Mountain (Hangul: 북악산; Hanja: 北岳山), north of the downtown area[35]), the gates remain near the downtown district of Seoul, including most notably Sungnyemun (commonly known as Namdaemun) and Heunginjimun (commonly known as Dongdaemun).[36] During the Joseon dynasty, the gates were opened and closed each day, accompanied by the ringing of large bells at the Bosingakbelfry.[37] In the late 19th century, after hundreds of years of isolation, Seoul opened its gates to foreigners and began to modernize. Seoul became the first city in East Asia to introduce electricity in the royal palace, built by the Edison Illuminating Company[38] and a decade later Seoul also implemented electrical street lights.[39]

Much of the development was due to trade with foreign countries like France and the United States. For example, the Seoul Electric Company, Seoul Electric Trolley Company, and Seoul Fresh Spring Water Company were all joint Korean–American owned enterprises.[40] In 1904, an American by the name of Angus Hamilton visited the city and said, "The streets of Seoul are magnificent, spacious, clean, admirably made and well-drained. The narrow, dirty lanes have been widened, gutters have been covered, roadways broadened. Seoul is within measurable distance of becoming the highest, most interesting and cleanest city in the East."[41]

After the annexation treaty in 1910, the Empire of Japan annexed Korea and renamed the city Gyeongseong ("Kyongsong" in Korean and "Keijo" in Japanese). Japanese technology was imported, the city walls were removed, some of the gates demolished. Roads became paved and Western-style buildings were constructed. The city was liberated by US forces at the end of World War II.[32]

In 1945, the city was officially named Seoul, and was designated as a special city in 1949.[32]

During the Korean War, Seoul changed hands between the Russian/Chinese-backed North Korean forces and the American-backed South Korean forces several times, leaving the city heavily damaged after the war. The capital was temporarily relocated to Busan.[32] One estimate of the extensive damage states that after the war, at least 191,000 buildings, 55,000 houses, and 1,000 factories lay in ruins. In addition, a flood of refugees had entered Seoul during the war, swelling the population of the city and its metropolitan area to an estimated 1.5 million by 1955.[42]

Following the war, Seoul began to focus on reconstruction and modernization. As Korea's economy started to grow rapidly from the 1960s, urbanization also accelerated and workers began to move to Seoul and other larger cities.[42] From the 1970s, the size of Seoul administrative area greatly expanded as it annexed a number of towns and villages from several surrounding counties.[43]

Seoul is in the northwest of South Korea. Seoul proper comprises 605.25 km2 (233.69 sq mi),[2] with a radius of approximately 15 km (9 mi), roughly bisected into northern and southern halves by the Han River. The Han River and its surrounding area played an important role in Korean history. The Three Kingdoms of Korea strove to take control of this land, where the river was used as a trade route to China (via the Yellow Sea).[46] The river is no longer actively used for navigation, because its estuary is located at the borders of the two Koreas, with civilian entry barred. Historically, the city was during the Joseon dynasty bounded by the Seoul Fortress Wall, which stretched between the four main mountains in central Seoul: Namsan, Naksan, Bukhansan and Inwangsan. The city is bordered by eight mountains, as well as the more level lands of the Han River plain and western areas. Due to its geography and to economic development policies, Seoul is a very polycentric city. The area that was the old capital in the Joseon dynasty, and mostly comprises Jongno District and Jung District, constitutes the historical and political center of the city. However, for example, the city's financial capital is widely considered to be in Yeouido, while its economic capital is Gangnam District.

Under the Köppen climate classification, Seoul has a humid continental climate, also bordering a humid subtropical climate. The suburbs of Seoul are generally cooler than the center of Seoul because of the urban heat island effect.[47] Summers are generally hot and humid, with the East Asian monsoon taking place from June until September. August, the warmest month, has average high and low temperatures of 29.6 and 22.4 °C (85 and 72 °F) with higher temperatures possible. Winters are usually cold to freezing with average January high and low temperatures of 1.5 and −5.9 °C (34.7 and 21.4 °F) and are generally much drier than summers, with an average of 24.9 days of snow annually. Sometimes, temperatures drop dramatically to below −10 °C (14 °F), and on some occasions as low as −15 °C (5 °F) in the mid winter period of January and February. Temperatures below −20 °C (−4 °F) have been recorded.[48]

According to the Environmental Performance Index 2016, South Korea ranked 173rd out of 180 countries in terms of air quality. More than 50 percent of the populations in South Korea exposed to dangerous levels of fine dust.[53][54]

Since the early 1960s, the Ministry of Environment has implemented a range of policies and air pollutant standards to improve and manage air quality for its people.[60] The "Special Act on the Improvement of Air Quality in the Seoul Metropolitan Area" was passed in December 2003. Its 1st Seoul Metropolitan Air Quality Improvement Plan (2005-2014) focused on improving the concentrations of PM10 and nitrogen dioxide by reducing emissions.[61] As a result, the annual average PM10 concentrations decreased from 70.0 μg/m3 in 2001 to 44.4 μg/m3 in 2011[62] and 46 μg/m3 in 2014.[57] As of 2014, the annual average PM10 concentration was still at least twice than that recommended by the WHO Air Quality Guidelines.[58] The 2nd Seoul Metropolitan Air Quality Improvement Plan (2015–2024) added PM2.5 and ozone to its list of managed pollutants.[63]

Asian dust, emissions from Seoul and in general from the rest of South Korea, as well as emissions from China, all contribute to Seoul's air quality.[56][64] A partnership between researchers in South Korea and the United States is conducting an international air quality field study in Korea (KORUS-AQ) to determine how much each source contributes.[65]

Seoul is divided into 25 gu (Hangul: 구; Hanja: 區) (district).[66] The gu vary greatly in area (from 10 to 47 km2 or 3.9 to 18.1 sq mi) and population (from fewer than 140,000 to 630,000). Songpa has the most people, while Seocho has the largest area. The government of each gu handles many of the functions that are handled by city governments in other jurisdictions. Each gu is divided into "dong" (동; 洞) or neighbourhoods. Some gu have only a few dong while others like Jongno District have a very large number of distinct neighbourhoods. Gu of Seoul consist of 423 administrative dongs (행정동) in total.[66]Dong are also sub-divided into 13,787 tong (통; 統), which are further divided into 102,796 ban in total.

Seoul proper is noted for its population density, which is almost twice that of New York and eight times greater than Rome. Its metropolitan area was the most densely populated in the OECD in Asia in 2012, and second worldwide after that of Paris.[67] As of 2015, the population was 9.86 million,[68] in 2012, it was 10,442,426.

[69] As of the end of June 2011, 10.29 million Republic of Korea citizens lived in the city. This was a .24% decrease from the end of 2010. The population of Seoul has been dropping since the early 1990s, the reasons being the high costs of living, urban sprawing to Gyeonggi region's satellite bed cities and an aging population.[68]

As of 2016, the number of foreigners living in Seoul was 404,037, 22.9% of the total foreign population in South Korea.[70] As of June 2011, 186,631 foreigners were Chinese citizens of Korean ancestry. This was an 8.84% increase from the end of 2010 and a 12.85% increase from June 2010. The next largest group was Chinese citizens who are not of Korean ethnicity; 29,901 of them resided in Seoul. The next highest group consisted of the 9,999 United States citizens who were not of Korean ancestry. The next highest group were the Republic of China (Taiwan) citizens, at 8,717.[71]

Seoul is the business and financial hub of South Korea. Although it accounts for only 0.6 percent of the nation's land area, 48.3 percent of South Korea's bank deposits were held in Seoul in 2003,[74] and the city generated 23 percent of the country's GDP overall in 2012.[75] In 2008 the Worldwide Centers of Commerce Index ranked Seoul No.9.[76] The Global Financial Centres Index in 2015 listed Seoul as the 6th financially most competitive city in the world.[77]The Economist Intelligence Unit ranked Seoul 15th in the list of "Overall 2025 City Competitiveness" regarding future competitiveness of cities.[78]

Seoul hosts large concentration of headquarters of International companies and banks, including 15 companies on fortune 500 list such as Samsung, LG and Hyundai.[83] Most bank headquarters and the Korea Exchange are located in Yeouido (Yeoui island),[79] which is often called "Korea's Wall Street" and has been serving as the financial center of the city since the 1980s.[84] The Seoul international finance center & SIFC MALL, Hanhwa 63 building, the Hanhwa insurance company head office. Hanhwa is one of the three largest Korean insurance companies, along with Samsung Life and Gangnam & Kyob life insurance group.

The largest wholesale and retail market in South Korea, the Dongdaemun Market, is located in Seoul.[85]Myeongdong is a shopping and entertainment area in downtown Seoul with mid- to high-end stores, fashion boutiques and international brand outlets.[86] The nearby Namdaemun Market, named after the Namdaemun Gate, is the oldest continually running market in Seoul.[87]

Korea World Trade Center Complex, which comprises COEX mall, congress center, 3 Inter-continental hotels, Business tower (Asem tower), Residence hotel, Casino and City airport terminal was established in 1988 in time for the Seoul Olympics . 2nd World trade trade center is planning at Seoul Olympic stadium complex as MICE HUB by Seoul city. Ex-Kepco head office building was purchased by Hyundai motor group with 9billion USD to build 115-storey Hyundai GBC & hotel complex until 2021. Now ex-kepco 25-storey building is under demolition.

Seoul has been described as the world's "most wired city",[94] ranked first in technology readiness by PwC's Cities of Opportunity report.[95] Seoul has a very technologically advanced infrastructure.[96][97]

Seoul is among the world leaders in Internet connectivity, being the capital of South Korea, which has the world's highest fibre-opticbroadband penetration and highest global average internet speeds of 26.1 Mbit/s.[98][99] Since 2015, Seoul has provided free Wi-Fi access in outdoor spaces through a 47.7 billion won ($44 million) project with Internet access at 10,430 parks, streets and other public places.[100] Internet speeds in some apartment buildings reach up to 52.5Gbit/s with assistance from Nokia, and though the average standard consists of 100 Mbit/s services, providers nationwide are rapidly rolling out 1Gbit/s connections at the equivalent of 20 USD per month.[101] In addition, the city is served by the KTXhigh-speed rail and the Seoul Subway, which provides 4G LTE, WiFi and DMB inside subway cars. 5G will be introduced commercially in March 2019 in Seoul.

The traditional heart of Seoul is the old Joseon dynasty city, now the downtown area, where most palaces, government offices, corporate headquarters, hotels, and traditional markets are located. Cheonggyecheon, a stream that runs from west to east through the valley before emptying into the Han River, was for many years covered with concrete, but was recently restored by an urban revival project in 2005.[102]Jongno street, meaning "Bell Street", has been a principal street and one of the earliest commercial streets of the city,[103][104] on which one can find Bosingak, a pavilion containing a large bell. The bell signaled the different times of the day and controlled the four major gates to the city. North of downtown is Bukhan Mountain, and to the south is the smaller Namsan. Further south are the old suburbs, Yongsan District and Mapo District. Across the Han River are the newer and wealthier areas of Gangnam District, Seocho District and surrounding neighborhoods.

Urban and civil planning was a key concept when Seoul was first designed to serve as a capital in the late 14th century. The Joseon dynasty built the "Five Grand Palaces" in Seoul – Changdeokgung, Changgyeonggung, Deoksugung, Gyeongbokgung and Gyeonghuigung – all of which are located in Jongno and Jung Districts. Among them, Changdeokgung was added to the UNESCO World Heritage List in 1997 as an "outstanding example of Far Eastern palace architecture and garden design". The main palace, Gyeongbokgung, underwent a large-scale restoration project.[106] The palaces are considered exemplary architecture of the Joseon period. Beside the palaces, Unhyeongung is known for being the royal residence of Regent Daewongun, the father of Emperor Gojong at the end of the Joseon Dynasty.

Seoul has been surrounded by walls that were built to regulate visitors from other regions and protect the city in case of an invasion. Pungnap Toseong is a flat earthen wall built at the edge of the Han River, which is widely believed to be the site of Wiryeseong. Mongchon Toseong (Hangul: 몽촌토성; Hanja: 蒙村土城) is another earthen wall built during the Baekje period that is now located inside the Olympic Park.[33] The Fortress Wall of Seoul was built early in the Joseon dynasty for protection of the city. After many centuries of destruction and rebuilding, about ⅔ of the wall remains, as well as six of the original eight gates. These gates include Sungnyemun and Heunginjimun, commonly known as Namdaemun (South Great Gate) and Dongdaemun (East Great Gate). Namdaemun was the oldest wooden gate until a 2008 arson attack, and was re-opened after complete restoration in 2013.[107] Situated near the gates are the traditional markets and largest shopping center, Namdaemun Market and Dongdaemun Market.

There are also many buildings constructed with international styles in the late 19th and early 20th centuries. The Independence Gate was built in 1897 to inspire an independent spirit. Seoul Station was opened in 1900 as Gyeongseong Station.

Various high-rise office buildings and residential buildings, like the Gangnam Finance Center, the Tower Palace, Namsan Seoul Tower, and the Lotte World Tower, dominate the city's skyline. The tallest building is Lotte World Tower, reaching a height of 555m. It opened to the public in April 2017.

The War Memorial, one of nine municipal museums in Seoul, offers visitors an educational and emotional experience of various wars in which Korea was involved, including Korean War themes.[114][115] The Seodaemun Prison is a former prison built during the Japanese occupation, and is currently used as a historic museum.[116]

There are also religious buildings that take important roles in Korean society and politics. The Wongudan altar was a sacrificial place where Korean rulers held heavenly rituals since the Three Kingdoms period. Since the Joseon dynasty adopted Confucianism as its national ideology in the 14th century, the state built many Confucian shrines. The descendants of the Joseon royal family still continue to hold ceremonies to commemorate ancestors at Jongmyo. It is the oldest royal Confucian shrine preserved and the ritual ceremonies continue a tradition established in the 14th century. Munmyo and Dongmyo were built during the same period. Although Buddhism was suppressed by the Joseon state, it has continued its existence. Jogyesa is the headquarters of the Jogye Order of Korean Buddhism. Hwagyesa and Bongeunsa are also major Buddhist temples in Seoul.

The Myeongdong Cathedral is a landmark of the Myeongdong, Jung District and the biggest Catholic church established in 1883. It is a symbol of Catholicism in Korea. It was also a focus for political dissent in the 1980s. In this way the Roman Catholic Church has a very strong influence in Korean society.

Despite the city's population density, Seoul has a large quantity of parks. One of the most famous parks is Namsan Park, which offers recreational hiking and views of the downtown Seoul skyline. The N Seoul Tower is located at Namsan Park. Seoul Olympic Park, located in Songpa District and built to host the 1988 Summer Olympics is Seoul's largest park. Amongst the other largest parks in the city are Seoul Forest, Dream Forest, Children's Grand Park and Haneul Park. The Wongaksa Pagoda 10 tier pagoda is situated In Tapgol Park, a small public park with an area of 19,599 m2 (210,962 sq ft). Areas around streams serve as public places for relaxation and recreation. Tancheon stream and the nearby area serve as a large park with paths for both walkers and cyclists.
Cheonggyecheon, a stream that runs nearly 6 km (4 mi) through downtown Seoul, is popular among both Seoul residents and tourists. In 2017 the Seoullo 7017 Skypark opened, spanning diagonally overtop Seoul Station.

There are also many parks along the Han River, such as Ichon Hangang Park, Yeouido Hangang Park, Mangwon Hangang Park, Nanji Hangang Park, Banpo Hangang Park, Ttukseom Hangang Park and Jamsil Hangang Park.
The Seoul National Capital Area also contains a green belt aimed at preventing the city from sprawling out into neighboring GyeonggiProvince. These areas are frequently sought after by people looking to escape from urban life on weekends and during vacations.
There are also various parks under construction or in project, such as the Gyeongui Line Forest Trail, Seoul Station 7017, Seosomun Memorial Park and Yongsan Park.

Seoul has a well developed transportation network. Its system dates back to the era of the Korean Empire, when the first streetcar lines were laid and a railroad linking Seoul and Incheon was completed.[121] Seoul's most important streetcar line ran along Jongno until it was replaced by Line 1 of the subway system in the early 1970s. Other notable streets in downtown Seoul include Euljiro, Teheranno, Sejongno, Chungmuro, Yulgongno, and Toegyero. There are nine major subway lines stretching for more than 250 km (155 mi), with one additional line planned. As of 2010[update], 25% of the population has a commute time of an hour or more.

Seoul's bus system is operated by the Seoul Metropolitan Government (S.M.G.), with four primary bus configurations available servicing most of the city. Seoul has many large intercity/express bus terminals. These buses connect Seoul with cities throughout South Korea. The Seoul Express Bus Terminal, Central City Terminal and Seoul Nambu Terminal are located in the district of Seocho District. In addition, East Seoul Bus Terminal in Gwangjin District and Sangbong Terminal in Jungnang District handles traffics mainly from Gangwon and Chungcheong provinces.

Seoul is connected to every major city in South Korea by rail. Seoul is also linked to most major South Korean cities by the KTX high-speed train, which has a normal operation speed of more than 300 km/h (186 mph). Another train that stops at all major stops are the Mugunghwa and Saemaeul trains. Major railroad stations include:

Cycling is becoming increasingly popular in Seoul and in the entire country. Both banks of the Han River have cycling paths that run all the way across the city along the river. In addition, Seoul introduced in 2015 a bicycle-sharing system named Ddareungi (and named Seoul Bike in English).[122]

Compulsory education lasts from grade 1-9 (six years of elementary school and 3 years of middle school).[123] Students spend six years in elementary school, three years in middle school, and three years in high school. Secondary schools generally require students wear uniforms. There is an exit exam for graduating from high school and many students proceeding to the university level are required to take the College Scholastic Ability Test that is held every November. Although there is a test for non-high school graduates, called school qualification exam, most Koreans take the test.

^"Seoul". Encyclopædia Britannica. 2009. Retrieved 6 September 2009. The city was popularly called Seoul in Korean during both the Chosŏn (Yi) dynasty (1392–1910) and the period of Japanese rule (1910–45), although the official names in those periods were Hansŏng (Hanseong) and Kyŏngsŏng (Gyeongseong), respectively.

^"South Korea near bottom of world survey of air quality". The Korea Herald. May 16, 2016. South Korea ranked 173rd out of 180 countries in terms of air quality, the Environmental Performance Index 2016 rankings showed Monday. ... A report said that 1.3 billion people exposed to poor air quality lived in East Asian countries, with more than 50 percent of the populations in South Korea and China exposed to dangerous levels of fine dust.